Query SQL external tables

This article describes how to query external tables based on SQL tables.

You can query a SQL external table just as you would query an Azure Data Explorer or a table in a KQL Database.

How it works

Azure SQL external table queries are translated from Kusto Query Language (KQL) to SQL. The operators after the external_table function call, such as where, project, count, and so on, are pushed down and translated into a single SQL query to be executed against the target SQL table.

Example

For example, consider an external table named MySqlExternalTable with two columns x and s. In this case, the following KQL query is translated into the following SQL query.

KQL query

external_table(MySqlExternalTable)
| where x > 5 
| count

SQL query

SELECT COUNT(*) FROM (SELECT x, s FROM MySqlTable WHERE x > 5) AS Subquery1